1. Field of the Invention
The present invention relates to a microfabrication method and devices fabricated using the same. More particularly, the invention pertains to a microfabrication method suitable for fabricating microstructures comprising parts made of high-temperature superconductor material or SrTiO3 monocrystalline material, e.g., a microfabrication method suitable for fabricating microstructure devices such as a magnetic force microscope probe and a magnetic field sensor.
2. Description of the Related Art
Recent years have seen significant advances in a variety of applications using a micromachining technique based on silicon semiconductor microfabrication processing. In these applications, silicon crystal anisotropic etching with an alkali etchant such as potassium hydroxide has been used as a basic microfabrication method (found in U.S. Pat. No. 3,765,969). More specifically, since an etching rate is substantially lower on a crystallographic plane (111) than on planes (100) and (110) under particular etching conditions, precision three-dimensional micromachining can be carried out using a proper mask. In the micromachining, it is common practice to use silicon as a material on account of convenience that the semiconductor microfabrication technique is applicable thereto in a similar fashion.
In the conventional semiconductor microfabrication technique mentioned above, however, no consideration is given to implementation of fabricating microstructures made of any material other than silicon, i.e., it is difficult to apply the conventional semiconductor microfabrication technique to fabrication of microstructures made of non-silicon material. In formation of a thin film of high-temperature superconductor, it is required to use a proper monocrystal substrate. In the case of forming a high-temperature superconductor thin film YBa2Cu3O7xe2x88x92xcex4, for example, a monocrystal substrate SrTiO3 is used to attain satisfactory results of fabrication. However, an etchant effective for SrTiO3 monocrystal, which is analogous to potassium hydroxide for silicon, has not been known heretofore. The SrTiO3 monocrystal is not etched at all by an etchant such as potassium hydroxide used for silicon crystal anisotropic etching.
For anisotropic etching, a physical etching method is available as well as a chemical etching method. In the physical etching method, however, an etching rate is relatively low. In particular, a material such as SrTiO3 monocrystal is hardly etched by the physical etching method under ordinary conditions for silicon etching. Even in the case of silicon etching, the physical etching method takes an impractically long period of time to accomplish penetration etching through a thick silicon substrate.
For silicon material, a physico-chemical etching method using a combination of plural kinds of special gases has been developed to attain an etching rate which is approximately 1000 times higher than that in a conventional method. Using the physico-chemical method, it is possible to accomplish silicon etching within a practically allowable period of time. In contrast, for SrTiO3 monocrystal material, such a desirable etching method has not yet been established.
Besides, the following approach has been proposed: After a thin film of SrTiO3 monocrystal is grown on a silicon substrate which allows anisotropic etching, a thin film of high-temperature superconductor YBa2Cu3O7xe2x88x92xcex4 is grown over the grown thin film of SrTiO3 monocrystal. However, satisfactory results have not yet been attained in this approach. The physical etching method is also disadvantageous in that a damage is likely to be involved in a processed surface and in that there is a difficulty in controlling an angle of processing. For instance, it is known that a Josephson junction can be provided by forming a step difference part on the surface of an SrTiO3 monocrystal substrate through physical etching and then growing a thin film of high-temperature superconductor thereon. However, since the performance of a junction formed using a step difference part largely depends on conditions of the angle and surface of the step difference part, it is not practicable to fabricate a Josephson junction device having high performance stability by using a step difference part formed through physical etching.
It is therefore an object of the present invention to provide a method of precise microfabrication of an SrTiO3 monocrystal substrate by growing a high-temperature superconductor thin film thereon.
Another object of the present invention is to provide a device comprising a part made of a high-temperature superconductor thin film fabricated by the above-mentioned method.
A further object of the present invention is to provide a device having a dielectric property of an SrTiO3 monocrystal substrate fabricated by the above-mentioned method.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.